The majority of medical records are protected under privacy laws, and most records aren't kept long term.
If you are seeking your medical records, or those of a recently deceased close relative (spouse, partner, parent, sibling or child), you can learn more on the Information and Privacy Commissioner of Ontario website.
If you are seeking historical medical records it will be a challenge as most no longer exist. Archives of Ontario has some records pertaining to medical personnel, psychiatric & tuberculousis records. Library & Archives Canada has some information on medical personnel.
What can psychiatric records offer? Heather Stovold shares her experience:
I had my first clue that Mental Health Records could be helpful when the Registration of my GG-Grandfather was made by the Minto Asylum. My GG-Grandfather had also been enumerated twice in the 1881 census, once at home with his family, and once in the Hamilton Asylum.
Doing a search in Google, I discovered a few websites about each Asylum, including pictures of the Asylum, and some general descriptions of the type of life led by the inmates. I discovered that my GG-Father had probably helped build the Minto Asylum, as he died there during the first years it was open.
Imagine my delight, when Google brought up a big article in the Ontario Archives on Psychiatric Records!
I then sent an information request form to the Ontario Archives with the information I had on the 2 dates that my GG-Father would have been in the 2 Asylums, with a request for any information available for those, and any other, stays.
What a mother lode of information! Although I didn't get any vital information I didn't already have, I found out that his sister (that I didn't know existed) had also been an inmate of an asylum - and it included her married name. I also got very descriptive information on his behaviour at the asylum from the patient casebook, including such tidbits as an escape during one of his commitments, that at least a few times he had been sent to the asylum from the Jail, that he was considered a dangerous lunatic. He appeared to spend a lot of time in his bed despondent, had periods of useful work, and at other times was very disruptive and abusive to the staff.
I have since gotten further back in my genealogy from researching the information I had gotten about his sister!
I definitely recommend using mental health records if you have reason to believe that an ancestor had ever been in an asylum!